Over the last twenty years, the demand for data network services has grown rapidly. Many large networks have been built by a number of providers to meet the voracious demand for bandwidth to handle data traffic.
Data networks are commonly used for inter alia transmission of electronic mail messages (hereinafter e-mail). According to Post Office Protocol (hereinafter POP) standard for e-mail handling, transmitted e-mail messages are routed to a centralized mail server facility. Those e-mail messages are warehoused at the centralized mail server until retrieved by their intended recipients. A user retrieves their e-mail messages from the mail server by sending an inquiry message via the network to the mail server asking if there is any mail stored there for them. Commonly these inquiry messages sent to the mail server are known as “POP checks” because they check for mail according to the Post Office Protocol. If the user's mail box is empty, then the mail server sends a negative response to the user telling him so. On the other hand, if the mail server is storing mail messages for the user, those messages are transmitted (in response to the POP check) to the user via the network.
One problem with large data networks where the clients are connected at all times without having to create a dial up connection is the large amount of network traffic due to frequent POP checks that users make (or, more typically, that the users' computers makes on the users' behalf) to see if there are any new e-mail messages waiting for them on the mail server. The use of a POP3 mail system in a wide area network (WAN) may result in a large amount of network traffic. This is not only a bandwidth problem, but also causes a substantial loading on the servers across the network that have to handle and route all this largely unproductive traffic. When a mail server is remote from the mail client, each POP3 request may require numerous hops to transverse the network, and response must travel the same distance.
It is largely unproductive traffic because the vast bulk of POP checks (over 90%, typically) result in negative responses because POP checks are generated much more frequently than the frequency with which e-mail messages arrive at the mail server. This is very inefficient. Significant traffic handling server load reduction, and some bandwidth savings, can be made if most POP checks are terminated close in the network to the sender.
Thus, what is needed is a scheme for reducing the number of POP checks that are transmitted over the network to the mail server.
Another e-mail related problem in networks is that the bandwidth demand resulting from e-mail traffic is concentrated during certain times of the day. In particular, the morning hours are a concentrated time for retrieval of e-mail messages from the mail server. These e-mail-generated spikes in bandwidth demand present network management challenges. One typical solution is to increase bandwidth capacity of the network to accommodate demand spikes completely. Obviously, this is an expensive and inefficient option because the added capacity will go largely unused (except in the event of demand spikes). Another typical solution is to simply permit poor network performance during periods when bandwidth demand spikes. Obviously, this option would be a source of irritation to the users of the network.
Thus, what is needed is a scheme to accommodate e-mail retrieval traffic without adding capacity that will go largely unused and without reducing network performance.